Change the standard path of images in TinyMCE, where can I find the init of this editor?

I know I can change the paths of tinyMCE to add a subdomain, see here:

https://stackoverflow.com/questions/56577520/change-default-image-path-in-tinymce

Only problem now is where can I find this init from the TinyMCE? I tried to find it but I cannot seem to find it. I’m working normally with JCE but I have to make sure the new image path works with TinyMCE, so I can hopefully change it for JCE as well, as it seems to be based on TinyMCE.

If someone could help me out, that would be awesome!